Staff at Madrid's Barajas airport are threatening to go on strike after allegedly being violently intimidated by a roving gang of 50 people who offer an unauthorized luggage shrink-wrap service to travellers.

Workers for Safebag, the official luggage-wrapping company at Adolfo Suárez Madrid Barajas airport, have filed a legal complaint after being "terrorized" by a gang of approximately 50 people of eastern European origin, according to Spanish daily El Confidencial.

They have called on Spanish airport operator Aena to put an end to the actions of the plastic-wrap pirates and have threatened to go on strike if action is not taken.

In the court documents they allege that the illegal luggage wrappers are mainly Romanians and Bulgarians, and name the supposed leader of the operation.

Safebag workers say that gang members have threatened them and put them in violent situations.

"Our staff have had enough. For over two years we have suffered at the hands of this gang who threaten our workers with knives and slash their car tyres in the car park, and surround our plastic wrapping stations so they can take the business at half the price", said Safebag representative Juan Rivas.

"Can anyone tell me how to motivate a worker who's frightened to come to work? We've been threatened many times. How can you work with sales staff who can't sell their products?" he added.

Aena licence Safebag to operate in Spanish airports in return for 33 per cent of the pre-tax revenues, a minimum of €2,941,737 ($3,664,500).

Due to the actions of the privateers, Rivas said that it might not reach the minimum, thus "putting at risk the jobs of 60 or 70 staff".

If Aena do not open an investigation into the allegations this week, unions have indicated that they will accuse them of complicity and go on protest in the terminal building.